The present invention relates to radiation beam therapy systems and more particularly to an improved system and procedure for repeatedly aligning a tumor or other desired tissue area in a patient with a radiation beam of the radiation beam therapy system. Such a system and procedure allows the desired tissure area, e.g., the tumor, to be positioned accurately relative to the radiation beam for any number of successive radiation treatments.
Radiation has been used for many years in an attempt to control cancer by killing cancerous cells. However, in order to be effective, the radiation absorbed by the selected cancerous cells (the "tumor") must be sufficient to kill the cancerous cells, while the radiation absorbed by surrounding non-cancerous cells must be kept at levels low enough to prevent permanent damage to the non-cancerous cells. As a consequence, a less than optimal total dose of radiation must frequently be used to reduce unacceptable normal tissue damage. What is clearly needed, therefore, is an approach for better controlling the radiation dose delivered to the body tissue, and more specifically for increasing the radiation dose delivered to the tumor, while reducing the radiation dose delivered to surrounding normal tissue.
It is known that heavy charged particles, such as protons, offer significant advantages over other forms of radiation, such as electrons, gamma rays, or X-rays, in controlling the radiation dose delivered to the body tissue. This is because protons of a specific energy have a definite range or penetration depth in matter. They lose energy by collisions with atoms, and finally stop, all within a few millimeters of a known depth. More significantly, they deposit most of their energy within a small distance of the end of this penetration depth, termed the Bragg peak after its discoverer. This penetration depth depends only on the energy of the protons. Hence, by carefully controlling the energy of a proton beam, and by directing the beam to a known tumor location, a good kill rate of cancerous cells can be achieved while largely sparing nearby healthy tissue.
To this end, radiation beam therapy systems, including proton beam delivery systems, are known in the art. See, e.g., Chu, W. "NCI Program Project Proposal," Lawrence Berkeley Laboratory, Oct. 14, 1987; Renner et al., "Wobbler Facility for Biomedical Experiments," Med. Phys., Vol. 14, No. 5, pp 825-34 (September/October 1987). However, such systems are generally cumbersome and/or inefficient to operate, or are limited in their ability to accurately direct the charged particle beam to all possible tumor locations. An improved proton beam delivery system has thus been proposed and is currently being built for installation at the Loma Linda University Medical Center in Loma Linda, Calif. Features of the Loma Linda system of interest to the present invention are described more fully in the following U.S. Patent Applications:
1. Ser. No. 07/163,611, filed Mar. 3, 1988, entitled "Multi-Station Proton Beam Therapy System" now U.S. Pat. No. 4,870,287, PA0 2. Ser. No. 07/178,471, filed Apr. 17, 1988, entitled "Roller-Supported, Modular, Isocentric Gantry and Method of Assembly" now U.S. Pat. No. 4,917,344, issued Apr. 17, 1990, PA0 3. Ser. No. 07/187,722, filed Apr. 29, 1988, entitled "Method of Assembly and Whole Body, Patient Positioning and Repositioning Support For Use In Radiation Beam Therapy Systems" now U.S. Pat. No. 4,905,267 issued Feb. 27, 1990, PA0 4. Ser. No. 07/332,254, filed Mar. 31, 1989, entitled "Raster Scan Control System For A Charged Particle Beam."
All of the above-identified patent applications are assigned to Loma Linda University Medical Center, as is the instant application. Further, all of these applications are incorporated herein by reference.
Despite the advantages of proton therapy, however, such advantages are of little consequence if the proton beam cannot be accurately and repeatedly directed to the desired tumor location. The beam must be accurately directed to the tumor location in order to prevent damage to surrounding tissue. The beam must be repeatedly directed to the tumor location because exposure of the cancerous cells to the proton beam is generally administered though a series of exposure treatments, typically given several days or weeks apart from each other.
Unfortunately, unlike X-rays and some other forms of radiation, the proton beam does not create an image that can be used to help in the alignment process. Hence, in order to accurately direct the beam to a selected tissue location, other image-creating techniques must be used to provide the requisite alignment information. Further, in order to assure that the requisite alignment can be achieved over and over again, such image-creating techniques must utilize a repeatable reference image, or equivalent reference data, that provides the necessary baseline reference informatioin for future alignments. The present invention is directed to a system and procedure that accomplishes these goals.